THE PRESENT INVENTION relates to a safety belt buckle.
It is well known to provide a safety belt buckle which receives a tongue connected to part of a safety belt and retains the tongue within the buckle. The buckle usually has a push button which can be manually operated in order to release the tongue from the buckle.
The tongue is usually retained within the buckle by means of a latch or locking element which is movable between a latching position and a release position. This invention relates to a particular type of buckle known as a "servo buckle" in which the latch or locking element will tend to move to the release position when the tongue is moved in a direction tending to withdraw it from the buckle i.e. when tension is applied to the safety belt. In this type of buckle a second locking element is provided in order to retain the latch or main locking element in the locking position, the second locking element being movable by way of the push button so as to permit the latch or main locking element to move to the release position.
In some servo buckles the push button and the second locking element move in the same direction when the main locking element is moved to the release position and with this type of design the buckle can only be opened by a force acting to move the push button and/or the second locking element in one direction.
In other designs of servo buckle the push button and the second locking element move in opposite directions when the main locking element is to be moved to the release position and with this type of buckle design the buckle could be opened as a result of forces acting either in the direction of movement of the push button or of the second locking element. These components normally move parallel to the longitudinal axis of the buckle. Thus, the buckle must be able to withstand high accelerations in either direction along the main axis of the buckle. This is particularly important for buckles provided with a safety belt pre-tensioner device which, when activated, imparts a high acceleration to the buckle in one direction along its axis.
This invention is particularly concerned with servo buckles in which the push button moves in the opposite direction to the second locking element (when considered axially of the buckle) when the main locking element is to move to the release position.
With this type of servo buckle it is possible for the push button and the second locking element to be "mass-balanced", that it to say the mass of the push button and the second locking element and their positioning relative to each other within the buckle may be selected so that if the buckle is subjected to a high acceleration in either direction along its longitudinal axis the push button and the second locking element will act against each other to prevent movement of either component which could result in the main locking element being freed to move to the release position. Such an arrangement is considered as being "g-safe".
Various g-safe servo buckle designs are known and one such buckle is disclosed in DE-OS 3 833 483. In the embodiment shown in FIGS. 1 to 3 of this document the second locking element takes the form of a pair of levers which pivot about a vertical axis through the buckle. There is a fixed connection between a push button and the second locking element and also between a separate balancing mass and the second locking element. Whilst this arrangement is g-safe, the fixed connections between the push button and the second locking element means that the push button remains in a depressed position once it has been actuated in order to open the buckle. Such an arrangement is not acceptable to the automotive industry where it is required that the push button should return to its initial position after it has been pushed in in order to open the buckle.
Further g-safe servo buckle arrangements are disclosed in DE-OS 4 007 915 and DE-OS 4 007 916, but again the arrangements disclosed in these documents suffer from the same problems outlined above.